Device for obtaining a simultaneous movement and balancing of the pressplatens in a multi-platen hot press



Jan. 2, 1968 a. J. CARLSSON E AL 3,361,056

DEVICE FOR OBTAINING A SIMULTANEOUS MOVEMENT AND BALANCING OF THE PRESS'FLATENS IN A MULTI-PLATEN HOT PRESS Filed June 10, 1965 5 Sheets-Sheet 1 Fig] Jan. 2, 1968 B. J.'CARLSSON ET AL 3,361,056 ANCING OF DEVICE FOR OBTAINING A SIMULTANEOUS MOVEMENT AND EAL THE PRESS-PLATENS IN A MULTI-PLATEN HOT PRESS Filed June 10, 1965 s Sheets -Sh eet 2 Fig.3

Fig.2

1963 B. J. CARLSSON ET AL 3,361,056

DEVICE FOR QBTAINING A SIMULTANEOUS MOVEMENT AND BALANCING OF THE PRESS-PLATENS IN A MULTI-PLATEN HOT PEESS Filed June 10, 1965 Fig.5

i .T I T T oz. 0 1 z 1 I I T 21. 21. 21. 24 10s 1 103 I 2s 2s 2s 2B 5 Sheets-Sheet a United States Patent 3,361,056 DEVICE FOR OBTAINING A SIMULTANEOUS MOVEMENT AND BALANCING OF THE PRESS- PLATENS IN A MULTI-PLATEN HOT PRESS Bengt Johan Carlsson and Nils Evert Erling Book, Motala Verkstad, Sweden, assignors to Aktiebolaget Motala Verkstad, Motala Verkstad, Sweden, a corporation of Sweden Filed June 10, 1965, Ser. No. 462,959 Claims priority, application Sweden, June 12, 1964, 7,204/ 64 8 Claims. (Cl. 100-200) ABSTRACT OF THE DISCLOSURE A multi-platen hot press having a toggle mechanism between a fixed and movable press-table including an upper swinging lever coupled to the upper press-table, a lifting rod between the swinging lever and each press-platen and a fluid operated yieldable means on each lifting rod, 2. pressure fluid system being provided connected in common to a plurality of the yieldable means and including valve control means to regulate the operating pressure of a fluid supply to the plurality of yieldable means during movement of the press-platens such that the pressure can be adjusted to many different levels or be Zero during such movement.

The present invention relates to a device for obtaining a simultaneous movement and balancing of the pressplatens in a multi-platen hot press, and particularly for obtaining exactly the same operation cycle of the multiplatens at all levels or storeys. Such a press is substantially used in the manufacture of fibreboard, hardboard and the like.

The conventional multi-platen presses are characterized in that the openings between the platens are closed and opened one after the other and in that the press force when the" press is closed, on account of the weight of the platens, varies stepwise from storey to storey. The disadvantages of such an arrangement are:

(1) the relative velocity between adjacent press-platens during the stepwise closing will be the same as the velocity of the press table and when pressing dry, fibrous material, there is a risk that this material is blown out from the spaces between the platens when the press is closed;

(2) the contact time between the pressed material and the overlying press-platen is different in the various storeys which can lead to a deterioration of the quality of the pressed product;

(3) the surface pressure becomes lower in the upper storeys than in the lower storeys which results in a different density or thickness of the pressed product;

(4) the opening-velocity in each storey is the same as the velocity of the press table which often must be limited to prevent too high a suction of impurities into the spaces between the press-platens and the gloss plates which usually are provided at the lower sides of the platens. In certain presses such as, for pressing and drying fibreboard, it is conventional to have a wire-gauze or so-called interlining wire between the gloss plate and the press-platen to accumulate the impurities sucked in. This wire-gauze, however, impairs the heat transfer from the press-platen which further prolongs the press-cycle.

To avoid these disadvantages a mechanism is required which by closing and opening of the press gives the pressplatens a simultaneous movement which is such that an equally high relative velocity is obtained between all adjacent press-platens and which mechanism when contact is reached between the press-mass and the press-platens, has a lifting action on the platens with forces which have been adapted to their weight. The mechanism must, when contact is reached between the press-mass and the pressplatens, be yieldable so that it is not damaged by overload if one or more storeys have an incorrect filling or are empty. The mechanism must also allow a rapid closing of the press without any risk of jeopardizing the simultaneous closing movement on account of the acceleration forces which must act on the press-platens and can amount to many times their weight. Finally the mechanism shall cause a simultaneous opening from the start independently of any filling faults, thickness differences between the press-platens or the like as the suction of impurities only takes place during the first part of the opening movement.

Devices are known where the press-platens are provided with a simultaneous closing movement by means of four toggle mechanisms provided around the press each with a swinging lever pivotally mounted at its one end to the upper press-table of the press and at its other end to the upper end of a driving bar the lower end of which in the same way is mounted on the lower press table. At suitable places of the swinging levers are connected lifting rods in turn connected to the press-platens so that a simultaneous closing movement is obtained in all storeys when the lower press table is driven by the main machinery of the press. The use of this device is, however, limited to the theoretical case in which all fillings, press-platens, conveyor plates etc. have exactly the same thickness.

Devices are also known which, by means of hydraulic piston-cylinder devices with individual overflow valves, make the lifting rods yieldable when the rod forces exceed or fall below a certain preset value. Thus, if there is too great a filling in the uppermost storey, all lifting rods need to be extended, but they are subjected to an additional force above that which corresponds to the weight of the platens which results in a higher surface pressure on the press-mass in the upper storeys than in the lower storeys. If, however, on the contrary, a shortening is needed, clue to too great a filling in the lower storeys, the forces are reduced and the result is the opposite. These devices are not allowed to yield to the acceleration and retardation forces and if the press is closed and opened rapidly, they must be very rigid which is a disadvantage during the remaining cycle of the pressing operation. In the cases where these known devices have been used, it has been necessary to provide, in addition, other bulky means to limit the downward movement of the pressplatens.

To solve the above mentioned problem in connection with a device comprising a toggle mechanism between the fixed and movable press-table, a lifting rod between the upper swinging lever of the mechanism and each pressplaten and a fluid-operated yieldable means on each lifting rod, the device according to the invention is characterized in that the yieldable means is connected to a pressurefluid system the operating members of which are common for the said means of several lifting rods and the operating pressure can be adjusted to many different levels or be zero.

This device makes it possible to press, within technical limits, with any desired closing velocity and with any acceleration depending thereon, but with the greatest yieldability of the lifting means at the moment of contact and with lifting forces during the actual pressing operation which, within practical limits correspond to the weight of the platen. Moreover, the above is achieved with simultaneous opening of all storeys from the beginning of the opening, independently of any variations in thickness of the filling, press-platens or the like. Furthermore the device also makes it possible to exclude the conventional step-like support posts which hold the pressplatens at equal distances in relation to one another when a the press is open to facilitate the loading of the press. Thus, the present invention allows a pressing operation in a multi-platen press with equal short press-cycles as in a one-storey press and with the same result in all storeys.

The invention will be further described in connection with the embodiments shown in the attached drawings.

FIG. 1 is a vertical view of the device according to the invention and with the press-platens in section.

FIG. 2 shows partly in section the yieldable means.

FIG. 3 shows in the same way a simplified embodiment of the yieldable means.

FIG. 4 shows another simplified embodiment of the yieldable means.

FIG. 5 shows diagrammatically a hydraulic system for the operation of the device according to the invention.

In FIG. 1 there is shown for the sake of clearness, only a small portion of the press, namely an upper fixed presstable 1, a lower movable press-table 2 and a plurality of intermediate press-platens 3. The platens 3 define spaced levels or storeys in each of which is shown a press-mass 4 which has been inserted on a conveyor plate 5, and is disposed beneath a surface or gloss plate 6 with an interlining wire 7 associated therewith and secured by screws 8 to the overlying press-platen. Normally there is also a press-wire between the mass and the conveyor plate and Wear plate below the conveyor plate but this is not shown in the drawing in order not to encumber it with unnecessary detail. Preferably at four places of the circumference of the press there is a swinging lever 9 which is connected to the upper press-table 1 and to a driving rod 10 which is connected to the lower press table. Each press platen is connected to one end of a corresponding lifting rod 11. The other end of each lifting rod is connected to a hydraulic piston-cylinder device 12 which in turn is connected to the swinging lever 9.

Each piston-cylinder device comprises, as shown in FIG. 2, a cylinder 13, a lower end wall 14 and an upper end wall 15 and a lower piston 16 with a piston rod 17 and an upper piston 18 with a piston rod 19 having a nut 20. The upper piston rod has a central bore 21 communieating with the space between the pistons. The cylinder is provided with two pivots 23 for the mounting of the cylinder in the swinging lever 9. Through one of the pivots there is a bore 24 leading to an upper pressure space 25 and the other pivot is provided with a bore 26 leading to a lower pressure space 27. The lower piston rod 17 is connected to the lifting rod 11 by means of a double threaded sleeve 28. The upper piston rod 19 is free. In the lower end wall there is provided a bushing 29 which is fixed by a washer 30 and is surrounded by an outer pressure space 31 with which a bore 32 in the end wall communicates. To seal the various pressure spaces there are shown a number of gaskets which all have the reference 33.

All the upper pressure spaces 25 communicate with a conduit 0 (FIG. 5), all the lower pressure spaces 27 with a conduit U, all the outer pressure spaces 31 with a conduit Y and all the pressure spaces 22 between the pistons with a conduit T in a hydraulic system common to the whole device and situated at any desired place easily accessible for service and protected against damage. In the present case the hydraulic system is driven by a driving unit 101 comprising a pump PF with constant deplacement driven by an electric motor M. This pump draws hydraulic liquid from a tank 102 and its pressure side is in communication with the conduit U and with valves 103 which can lead the whole or a portion of the pump flow through either of two overflow valves 104. The pressure side of the pump is also in direct communication with a further overflow valve 104 which is adjusted for a higher pressure than the other overflow valves 104. The pressure in the conduit U is thus determined by the adjustment of this overfiow valve. The conduit 0 can be connected to the pressure side of the pump by means of a valve 105 so that the pressure in the conduit becomes 4. the same as in the conduit U, or to the tank in which case the pressure becomes zero. The same arrangement prevails in the conduit Y. Finally, the conduit T is always connected to the tank 102 of the system and thus without any pressure.

The hydraulic equipment is so constructed that independently of the direction of flow it can maintain several different pressure levels in the conduit U, while the pressure in the conduit T is zero, and the pressures in the conduits O and Y are either the same as in the conduit U or equal to zero. The pressures are varied during the pressing operation in the following way.

(1) During the first part of the closing movement when the acceleration of the press-platens necessitates great pulling forces in the lifting rods, the pressure spaces 25 and 27 are fed with -a high pressure, e.g. seven times that pressure which corresponds to the weights of the platens. Thereby the two pistons are pressed towards each other with a great force, but on account of the fact that the downward movement of the upper piston rod is limited by the nut 20 the lower piston can take up the great pulling forces which are transferred from the lifting rod by means of the piston rod.

(2) After the short acceleration movement when the platens have reached a more constant velocity the pressure in the pressure spaces 25 and 27 is lowered to a lower value, e.g. 1.4 times that pressure which corresponds to the weights of the platens. Hereby the pistons are still pressed against each other and the nut on the upper piston rod rests against the upper end wall, until contact is reached between the press-mass and press-platens. If, thereafter, due to uneven filling one or several lifting rods would need to be extended, the piston-cylinder devices yield since the lower piston can be moved downwards from the upper piston by overcoming that resistance which corresponds to the hydraulic pressure in the space 27. If on the contrary a shortening of the lifting rods is needed, because the pulling force has fallen to zero, the piston-cylinder devices yield without any resistance due to the fact that both pistons move upwardly in the cylinder.

(3) When contact has been reached in all storeys of the press and the compression of the mass has started, the pressure is lowered in the upper pressure space 25 to zero and in the lower pressure space 27 to a value corresponding to the weight of the press-platens. Thus the press-platens are within practical limits wholly balanced, regardless of whether the piston-cylinder devices have been extended or shortened and about the same sur face pressure is obtained in all storeys of the press.

(4) Just before the press is to be opened the outer pressure space 31 is subjected to such a high pressure that the bushing 29 is compressed and clamps the lower piston rod 17 in the position it is in at this moment. Preferably, this takes place by maintaining the balancing pressure in the pressure space 27 so that the requirement on the clamping force is reduced. The piston-cylinder devices are now unyieldable for the forces which can be expected to occur in the lifting rods during the first part of the opening of the press, and the complete opening is started.

(5) When the press has been opened sufficiently so that the risk of sucking in impurities no longer exists, the pressure is lowered in the outer pressure space 31 while the pressure spaces 25 and 27 are supplied with the same pressure so that the pistons return to the positions they had at the start of the pressing cycle.

(6) When the press-table reaches its lower position and momentarily stops, the retardation of the press-platens is limited to what corresponds to the pressure supplied to the pressure spaces 25 and 27. After braking, the same pressure returns the press-platens to their original positions and the press is ready for a new charging.

The invention is not limited to the described embodiment and the described pressing method but can, if the actual pressing process allows or needs, be simplified or aserasa modified. Thus if the requirements on an equal surface pressure in the press are small and an exactly simultaneous opening is not required, the piston cylinder devices can be constructed more simply such as shown in FIG. 3 in which the upper piston and the upper piston rod with the associated nut have been omitted. In this case the lower piston rod is provided with an elongated opening 34 for its connection to the lifting rod by means of a pin 35, which arrangement allows a resistance-free shortening of the distance between press-platen and pistoncylinder device. In this case, the space above the piston is connected, by means of a bore 36 in one of the pivots, to a conduit T in a simplified hydraulic system common to all devices, while the lower pressure space is connected, in the same way as before, to a conduit U. This hydraulic system operates such that the pressure in the conduit T always is zero whereas in the conduit U, during the acceleration period, there is maintained first a high pressure and thereupon a second lower pressure. The first pressure is high enough to withstand the acceleration forces and the second pressure great enough to withstand the forces which the press-platens exert on the lifting rods without the piston losing its contact with the upper end wall.

Another simplified embodiment of the yieldable means, in such cases where the requirements of an equal surface pressure in all storeys can be disregarded but where it is required to obtain a simultaneous closing and an exactly simultaneous opening of the press, is shown in FIG. 4. Said means comprises a housing 37 which is provided with a brake bushing 38 held in position within the housing by means of a washer 39, and a rod 40 having a nut 41 axially movable in the brake bushing 38, said nut being intended to prevent the rod from being withdrawn from the bushing if a failure occurs. The housing is provided with two pivots 42 for the mounting of the housing 37 in the swinging lever. One of the pivots is provided with a bore 43 communicating with a pressure space 44 surrounding the bushing. The lower end of the rod is threaded for connection to a lifting rod 11 by means of a double-threaded sleeve 28. The pressure space 44 is connected to a conduit Y in a hydraulic system common to all piston-cylinder devices. When the pressure space 44 is put under pressure the bushing is compressed and clamps the rod with a force which increases with the pressure. Thus, the yieldability of the device can be varied by changing the pressure in the conduit Y.

The application is not limited to the described embodiments but can be varied in many ways within the scope of the invention.

What is claimed is:

1. In a multi-platen hot press having a fixed and a movable press-table and a plurality of press-platens therebetween a device for obtaining a simultaneous movement and balancing of the press-platens, comprising a toggle mechanism between the fixed and movable press-table including an upper swinging lever coupled to one of the presstables, a lifting rod between the swinging lever and each press-platen and a fluid-operated yieldable means on each lifting rod, and a pressure-fluid system connected in common to a plurality of said yieldable means and including valve control means to control the operating pressure of a fluid supplied to said plurality of yieldable means during movement of the press-platens such that the operating pressure of the associated lifting rods can be adjusted to many different levels or be zero during such movement.

2. A device according to claim 1, wherein the yieldable means comprises a double-acting piston-cylinder device (12) including a piston (16) having a piston rod (17) connected to the associated lifting rod (11) and a cylinder (13) pivotally connected to the upper swinging lever (9), the piston and cylinder defining a pressure space (27 on the piston rod side of the piston and a pressure space (22) on the opposite side of the piston, the pressure fluid system comprising a pressure-free fluid conduit (T) and a variable pressure conduit (U), said space (27) being connected to fluid conduit (U), and the pressure space (22) on the other side of the piston being connected to pressure-free fluid-conduit (T).

3. A device according to claim 2, wherein the pistoncylinder device (12) further comprises a free-piston (18) including a piston rod (19) which passes through the cylinder end wall (15) opposite to the first piston (16) and the movement of which towards the first piston is limited, piston (18) and cylinder (15) defining a pressure space (25 on the piston rod side of the free-piston (18), said pressure fluid system comprising a further variable pressure conduit 0 connected to the conduit U to be at the same pressure thereat or zero, said space (25) being connected to fluid conduit 0.

4. A device according to claim 3, wherein the yieldable means comprises a fluid pressure operated brake bushing (29) around the piston rod (17) connected to the lifting rod (11), a pressure space (31) being formed around the brake bushing and connected to a further fluid conduit (Y) having the same pressure as the fluid conduit (U) or zero pressure.

5. A device according to claim 2, wherein each cylinder (13) comprises a pair of pivots (23) connected to the swinging lever, at least one pivot being provided with a bore connected to an associated fluid conduit (U) and to the pressure space (27) on the piston rod side of the piston.

6. A device according to claim 2, wherein the piston rod (17) is connected to the lifting rod (11) by means of a pin (35) in one rod and passing through an elongated opening (34) in the other rod so that a resistancefree shortening of the distance between the press-platens (3) and the piston-cylinder device (12) is possible.

7. A device according to claim 1, wherein the yieldable means comprises a housing (37) pivotally connected to the upper swinging lever (9), a fluid operated brake bushing (38) situated in said housing (37), an axially displaceable rod (49) received in said bushing and connected to the associated lifting rod (11), the housing (37) defining a pressure space (44) around the brake bushing, the pressure fluid system including a fluid conduit (Y) with variable pressure or zero pressure connected to space (44-).

3. A device according to claim 7, wherein each housing (37) comprises a pair of pivots (42) connected to the swinging lever, at least one pivot being provided with a bore connected to as associated fluid conduit and to said pressure space (44).

References Cited UNITED STATES PATENTS 2,586,474 2/1952 Moore IDO -4 .00 2,884,032 4/1959 Thurnher 199 X 2,913,027 11/1959 Thurnher 10020O X 3,050,777 8/1962 Siempel Kamp 1816 3,202,088 8/1965 Hammon et al. 10O200 X LOUIS O. MAASSEL, Primary Examiner, 

